1. Field of the Invention
The present invention relates in general to a squeegee for use in a screen printing, and also to a squeegee device equipped with the squeegee.
2. Discussion of Related Art
In an operation with a screen printing machine, a print material is provided to be put on a surface of a mask screen which has print holes or apertures and which is placed on an object such as a board for providing a printed circuit board. A plate-like squeegee is slidably moved on the surface of the mask screen while the squeegee is held by a squeegee holding device in a forward tilted or inclined posture, i.e., in such a manner that the squeegee is inclined such that a distal free end portion of the squeegee is positioned on a rear side of a proximal end portion of the squeegee as viewed in a printing direction in which the squeegee is moved relative to the mask screen. With the sliding movement of the squeegee on the surface of the mask screen, the surface of the mask screen is wiped by the squeegee, namely, the print material arranged substantially in a line on the mask screen is carried or raked by the squeegee, so as to be forced or squeezed into the print apertures of the mask screen. The squeegee is commonly made of a rubber material having a high degree of elastic deformability which permits the squeegee to be held in close contact with the mask screen during the sliding movement, without separation of the squeegee from the mask screen even if a force acts on the squeegee in a direction away from the mask screen, so that the print material is reliably raked by the squeegee. That is, the rubber-made squeegee is held in close contact with the mask screen owing to the elastic deformation in its entirety, particularly, in its free distal end portion. Even in presence of the force acting on the squeegee in the direction away from the mask screen, the distal end portion of the squeegee is not separated from the mask screen, since the acting force causes simply a reduction in amount of the elastic deformation of the squeegee. However, the distal end portion of such a rubber-made squeegee having a high degree of elastic deformability tends to enter or bite into the apertures of the mask screen, so that the print material once received in the apertures is likely to be forced out of the apertures. Thus, the use of the rubber-made squeegee is likely to cause a problem that a sufficient amount of the print material is not printed on a print surface of the object, or a problem that the print material printed on the print surface of the object is not formed into a pattern corresponding to arrangement of the apertures.
The rubber-made squeegee may be replaced with a squeegee made of a metallic material which is more rigid or harder than a rubber material, for avoiding entrance or biting of a local part of the distal end portion of the squeegee into the apertures of the mask screen, so as to prevent the print material received in the apertures from being forced out of the apertures. Thus, owing to the use of the metallic squeegee, a desired amount of the print material is printed on the print surface of the object, and the print material printed on the print surface is accordingly formed into a desired pattern. However, the metallic squeegee is likely to be displaced in a direction away from the mask screen by a reaction force of the mask screen, so as to be easily separated from the mask screen. Due to the separation of the squeegee from the mask screen, the surface of the mask screen is not sufficiently wiped by the squeegee, so that some of the print material is left behind the squeegee, without being raked by the squeegee. While the above-described rubber-made squeegee can be elastically deformed particularly in its local portion, i.e., the distal end portion in which the squeegee is held in contact with mask screen, the metallic squeegee can not be locally deformed although the metallic squeegee has some degree of flexibility so as to be brought into contact with the mask screen with being somewhat bent in its entirety. Therefore, if a force acts on the metallic squeegee in a direction away from the mask screen, the metallic squeegee is undesirably separated from the mask screen, unlike the rubber-made squeegee which maintains its close contact with the mask screen owing to the sufficient amount of the elastic deformation of its distal end portion.
For solving the drawback indicated above, it is considered possible, for example, to adapt the squeegee to be slidably moved on the surface of the mask screen while the squeegee is held by the squeegee holding device in a rearward tilted or inclined posture, i.e., in such a manner that the distal end portion of the squeegee is positioned on a forward side of the proximal end portion of the squeegee as viewed in the printing direction in which the squeegee is moved relative to the mask screen. In this arrangement in which the distal end portion of the squeegee is constantly forced onto the mask screen during the sliding movement of the squeegee relative to the mask screen, the squeegee can be held in close contact with the mask screen even where the squeegee is made of a metallic material or other hard material. That is, in this arrangement, the metallic squeegee is not separated from the mask screen even when a reaction force is applied to the metallic squeegee from the mask screen, so that the metallic squeegee exhibits a satisfactory performance of raking the print material from the surface of the mask screen. Further, even in this arrangement in which the distal end portion of the squeegee is constantly forced onto the mask screen, the metallic squeegee which has a higher degree of hardness than the rubber-made squeegee does not allow considerable deformation of a local part of its distal end portion, and accordingly does not enter or bite into the apertures of the mask screen, whereby the print material once received in the apertures is prevented from being forced out of the apertures, leading to stable distribution of a sufficient amount of the print material into each of the apertures, and the consequently stable printing of the print material on the print surface of the object.
It is possible to adapt the squeegee to be elastically deformed in its entirety to be convexed toward the mask screen so as to be held in close contact at a larger area of its distal end portion with the mask screen, by increasing the degree of elastic deformability of the squeegee, for example, with an increase in the width of the squeegee, i.e., with an increase in the dimension of the squeegee in the printing direction. However, if the width of the squeegee is increased, the print material is likely to be mounted on the squeegee during the sliding movement of the squeegee on the surface of the mask screen. The print material mounted on the squeegee is eventually solidified without being received into the print apertures of the mask screen, thereby possibly producing a defectively printed product. That is, if the solidified print material is dropped from the squeegee onto unsolidified print material remaining on the mask screen, the solidified print material is mixed with the unsolidified print material, and the mixture is then forced into the apertures of the mask screen. The apertures are inevitably clogged with the mixture including the solidified print material, so that the print material is not allowed to be passed through the apertures so as to be printed on the object. This problem is encountered also in an arrangement in which the print material is accommodated in a space between a pair of squeegees such that the accommodated print material is moved together with the pair of squeegees while being raked by one of the squeegees which takes a rearward inclined posture.
It is an object of the present invention to provide a squeegee or squeegee device which is capable of efficiently raking a print material from a surface of a mask screen with minimized risk of biting of a distal end portion of the squeegee into print apertures of the mask screen, for thereby exhibiting an improved stability in a screen printing operation without producing a defectively printed product.
The above object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A squeegee for forcing a print material into apertures of a mask screen which is disposed on an object, so as to print the print material on the object, the squeegee comprising: (a) a plate body movable relative to the mask screen in sliding contact thereof with one of opposite surfaces of the mask screen which is remote from the object, while taking a rearward inclined posture in which the plate body is inclined such that a distal end portion of the plate body is positioned on a forward side of a proximal end portion of the plate body as viewed in a squeegee moving direction in which the plate body is moved relative to the mask screen; and (b) a bank portion provided on one of opposite surfaces of the plate body which is remote from the mask screen, and having a blocking surface which projects from the distal end portion of the plate body in a direction away from the mask screen, the bank portion being made of a material softer than a material of the plate body.
The above-described object, on which the print material to be printed, may be a substrate or board for providing a printed board in the form of a printed circuit board. The object may be a board which does not have any electric component mounted on the board, or may be a board which has some electric components mounted only on a surface opposite to a print surface. The print material may be an adhesive, a creamed solder or an ink, or alternatively a paste or other highly viscous fluid which does not include a solder component and which is to be applied to the board for facilitating a soldering operation. The mask screen may consist of a masking member made of a fiber material, a masking member principally made of a fiber material and reinforced by a metallic material, or a masking member made of a metallic material and commonly called as xe2x80x9cstencil maskxe2x80x9d. Either one of the plate body of the squeegee and the mask screen may be moved while the other of the plate body and the mask screen may be held stationary, or alternatively, the plate body and the mask screen may be moved in the respective directions which are opposite to each other. The bank portion may be simply held in close contact with the surface of the plate body, or alternatively may be fixed to the surface of the plate body by suitable fixing means. While the plate body of the squeegee is required to take the above-described rearward inclined posture at least during its sliding movement on the surface of the mask screen, the plate body may take other posture except during the sliding movement.
In the squeegee constructed according to this mode (1), the distal end portion of the plate body is held in contact with the mask screen in an elastic manner owing to the rearward inclined posture during a printing operation. By the sliding movement of the plate body and the mask screen relative to each other, the print material is pushed principally by the bank portion, and is also wiped or raked from the mask screen by the distal end portion of the plate body, so that the print material is squeezed or forced into the print holes or apertures. The distal end portion of the plate body thus serves to move the print material together with the plate body, and also serves to force the print material into the print apertures. The rearward inclined posture of the plate body which is maintained during the sliding movement is effective to enable the plate body to rake and carry the print material with high efficiency. Further, since the plate body is made of a comparatively rigid or hard material such as a metallic material as in the below-described (3), the distal end portion of the plate body does not enter or bite into the print apertures of the mask screen, so that the print material is prevented from being forced out of the apertures. Thus, a desired amount of the print material is printed on the print surface of the object, and the print material printed on the print surface is accordingly formed into a desired pattern corresponding to arrangement of the apertures. Further, the blocking surface provided in the distal end portion of the plate body serves to block the print material, preventing the print material to be mounted on the plate body. Since the bank portion having the blocking surface is made of a material softer than that of the plate body, the bank portion does not impede the elastic deformation of the plate body, permitting the distal end portion of the plate body to be brought into close contact with the mask screen so as to rake the print material from the mask screen. Consequently, the squeegee constructed according to this mode (1) is capable of efficiently raking the print material and accordingly achieving a screen printing operation with an improved stability, without causing a defective printing due to mounting of the print material on the plate body.
(2) A squeegee according to mode (1), wherein the bank portion has a blocking wall which projects from the distal end portion of the plate body in a direction away from the mask screen, and wherein the blocking surface is provided by a surface of the blocking wall.
The bank portion may be provided by a thick plate member which has a larger thickness than that of the plate body and which is superposed on and bonded to the one of the opposite surfaces of the plate body that is remote from the mask screen, so that the blocking surface is provided by a front end surface of the thick plate member. However, it is preferable that the blocking surface is provided by the front surface of the blocking wall as in the arrangement according to this mode (2), because the bank portion is elastically deformable more easily where the bank portion is principally provided by the wall than where the bank portion is provided by the thick plate member. The higher degree of elastic deformability of the bank portion facilitates the elastic deform of the plate body, thereby making it possible to bring the plate body into brought into close contact at a lager area of its distal end portion with the mask screen, and accordingly to permit the plate body to rake the print material from the surface of the mask screen with a higher efficiency. The arrangement of this mode (2) provides another advantage that the manufacturing cost of the squeegee can be reduced since the bank portion can be formed of a reduced amount of material.
(3) A squeegee according to mode (1) or (2), wherein the plate body is made of a metallic material.
In the squeegee constructed according to this mode (3) in which the plate body is made of a metallic material, the plate body is so hard that the distal end portion of the plate body is reliably prevented from entering or bite into the apertures of the mask screen. It is noted that the metallic plate body can be formed of a spring steel, a phosphor bronze or other material which has a suitable degree of elastic deformability or unbrittleness required for the plate body to be elastically deformable without risk of its fracture even where the plate body has a considerably reduced thickness, and also a suitable degree of hardness required for the plate body to satisfactorily rake the print material.
(4) A squeegee according to any one of modes (1)-(3), wherein the bank portion is made of a rubber.
(5) A squeegee according to any one of modes (1)-(3), wherein the bank portion is made of a material having substantially the same degree of elastic deformability as that of a rubber.
In the squeegee constructed according to each of modes (4) and (5), the bank portion is elastically further deformable, permitting the plate body to be elastically further deformable and thereby further facilitating the close contact of the distal end portion of the plate body with the surface of the mask screen. It is noted that there is known a soft synthetic resin as a material having the same degree of elastic deformability as that of a rubber.
(6) A squeegee device comprising: (a) the squeegee defined in mode (1); (b) a squeegee holder which holds the squeegee such that the other of the opposite surfaces of the plate body cooperates with the one of the opposite surfaces of the mask screen to define an angle not lager than 45xc2x0, and such that the blocking surface of the bank portion cooperates with the above-described one of the opposite surfaces of the mask screen to define an angle not larger than 90xc2x0; and (c) a moving device which is capable of moving the squeegee holder and the mask screen relative to each other while maintaining contact of the squeegee with the one of the opposite surfaces of the mask screen.
The angle defined by the surface of the plate body and the surface of the mask screen is preferably not larger than 45xc2x0, more preferably not larger than 30xc2x0, still more preferably not larger than 20xc2x0. In a printing operation with the squeegee device constructed according to this mode (6), the print material is first disposed on the mask screen so as to be exposed to the atmosphere (ambient space), and the print material is then carried by the squeegee when the squeegee is slidably moved on the mask screen. The carried print material is squeezed or forced into the print apertures, so as to be printed on the print surface of the object. In the squeegee of this mode (6) in which the blocking surface provided by the front surface of the bank portion is held in a forward tilted or inclined posture while the plate body is held in a rearward tilted or inclined posture, during the movement of the squeegee holder and the mask screen relative to each other, the print material is raked from the surface of the mask screen by the distal end portion of the plate body, and the print material is then forced into a wedge-shaped space which is defined by the blocking surface and the surface of the mask screen. The print material displaced into the wedge-shaped space is forced, toward the mask screen, by the blocking surface which cooperates with the surface of the mask screen to define an acute angle, i.e., an angle not larger than 90xc2x0. It is possible to further reduce the risk of biting of the distal end portion of the plate body into the apertures of the mask screen, by reducing the angle defined by the surface of the plate body and the surface of the mask screen. That is, it is possible to further reliably prevent the print material received in the apertures from being forced out of the apertures, with the reduction in the angle between the surface of the plate body and the surface of the mask screen.
(7) A squeegee device according to mode (6), further comprising a second moving device in addition to the moving device as a first moving device, the second moving device being capable of moving the squeegee holder between an operating position in which the squeegee is brought into contact with the above-described one of the opposite surfaces of the mask screen, and a non-operating position in which the squeegee is separated from the one of the opposite surfaces of the mask screen.
(8) A squeegee device according to mode (6) or (7), wherein the squeegee holder includes: a squeegee holding portion which holds the proximal end portion of the plate body; and a print-material pushing portion which is held in close contact with one of opposite ends of the bank portion that is remote from the plate body, and which has a print-material pushing surface that is contiguous to the blocking surface of the bank portion.
The pushing portion may be fixed to the end of the bank portion by an adhesive or other suitable means, or alternatively may be simply held in close contact with the end of the bank portion, without being fixed to the end of the bank portion. The pushing surface serves to push and move the print material along the surface of the mask screen. There is a case where the pushing surface also serves to force the print material into the apertures of the mask screen. In the squeegee device according to this mode (8) in which the pushing portion is held in close contact with the end of the bank portion, there is substantially no gap between the pushing portion and the end of the bank portion, through which the print material would be displaced onto the plate body. Thus, the print material is further reliably prevented from being mounted onto the plate body.
(9) A squeegee device according to any one of modes (6)-(8), wherein the bank portion of the squeegee has a blocking wall which projects from the distal end portion of the plate body in a direction away from the mask screen, and which has a surface forming the blocking surface, wherein the squeegee holder includes: a first member including a plate portion extending substantially in parallel with the plate body, and a plate-body seat portion projecting from one of opposite end portions of the plate portion, which one is positioned rearward of the other of the opposite end portions of the plate portion as viewed in the squeegee moving direction, toward the mask screen; and a second member which is removably attached to the first member and which cooperates with the first member to grip the proximal end portion of the plate body, wherein the plate portion of the first member is held in close contact at the other of the opposite end portions of the plate portion with an end portion of the blocking wall, while the proximal end portion of the plate body is gripped between the first and second members, and wherein the plate body, the blocking wall and the plate portion cooperate with the plate-body seat portion to constitute a hollow body which has a square shape in a cross section thereof.
The blocking wall may be fixed to the plate body by a welding, adhesive or other suitable means, or alternatively may be simply held in close contact with the plate body, without being fixed to the plate body. Similarly, the end portion of the plate portion of the first member may be fixed to the blocking wall, or alternatively may be simply held in close contact with the blocking wall, without being fixed to the blocking wall. In the squeegee device according to this mode (9) in which a void or space is formed on one of opposite sides of the plate body that is remote from the mask screen, the elastic deformation of the plate body is facilitated by this void or space, whereby the distal end portion of the plate body can be further reliably held in close contact with the mask screen, while the print material is prevented from being mounted onto the plate body.
(10) A squeegee device according to mode (9), wherein the squeegee holder further includes a third member which holds the first member and is held in close contact with one of opposite surfaces of the plate portion that is remote from the blocking wall, and wherein the third member cooperates with the first member to form a pushing surface that is adjacent to the blocking surface of the bank portion.
The third member may be fixed to the surface of the plate portion, or alternatively may be simply held in closed contact with the surface of the plate portion, without being fixed to the surface of the plate portion.
(11) A squeegee device comprising: (a) a pair of squeegees each of which is constituted by the squeegee defined in mode (1); (b) a squeegee holder which holds the pair of squeegees such that the blocking surfaces of the respective squeegees are opposed and parallel to each other, and such that the other of the opposite surfaces of the plate body of each of the pair of squeegees cooperates with the one of the opposite surfaces of the mask screen to define an angle not lager than 45xc2x0; and (b) a moving device which is capable of reciprocating the squeegee holder and the mask screen relative to each other in directions perpendicular to the blocking surfaces of the respective squeegees, while maintaining contact of each of the pair of squeegees with the above-described one of the opposite surfaces of the mask screen.
In the squeegee device of this mode (11), the printing material may be accommodated in a space between the pair of squeegees, and the accommodated print material is raked and moved with the movement of the pair of squeegees, so that a part of the print material corresponding to each of the apertures is forced into the aperture. During the reciprocation of the squeegee holder and the mask screen relative to each other, a rear side one of the squeegees, as viewed in a direction in which the pair of squeegees and the mask screen are currently moved relative to each other, serves to rake the print material, while a forward side one of the squeegees serves to prevent outflow of the print material from the space between the pair of squeegees. That is, the function of each of the pair of squeegees is changed each time the printing direction is changed. Thus, during the relative movement in both of the opposite directions, the print material is moved together with the squeegees while being raked from the mask screen, so that a part of the print material, which corresponds to each of the apertures, is forced into the aperture so as to be printed on the object. The above-described rear side one of the squeegees which serves to rake the print material takes a reward inclined posture, so that the plate body efficiently rakes the print material without entering or biting into the apertures while the bank portion prevents the print material from being mounted onto the plate body, for thereby achieving a print operation with high stability without causing a defective printing.
(12) A squeegee device according to mode (11), further comprising a pressure applying device capable of applying a pressure to the print material which is accommodated in a space between the blocking surfaces of the respective squeegees.
The pressure applying device, for example, may consist of a device which includes an extruding-member driving device for mechanically driving an extruding member so as to apply the pressure to the print material accommodated in above-described space, or alternatively may consist of a device which includes a pressurized-air supplying device for supplying a pressurized air to an upper portion of the space so as to apply the pressure to the print material.